1. Field of the Invention
The present invention relates generally to processes to obtain externally applied, out-of-plane operational load data using surface in-plane strain measurements on complex structures, particularly to real-time methods to calculate operational loads for complex structures, and most particularly an ultra-efficient process of calculating externally applied bending and torsional operational loads in real-time on complex structures using strain measurements provided by fiber Bragg grating technology.
An important by-product of this process is the efficient characterization of out-of-plane bending and torsional stiffness (material properties) of the complex structure.
2. Description of the Related Art
Currently, to obtain operational load data for complex structures, industry uses a very rigorous and time consuming design methodology that relies heavily on computational methods, such as finite element modeling (FEM). FEM requires that the structure to be designed/analyzed be analytically discretized into very small linear “elements.” Realistic structures are geometrically complex, as are the loads they are exposed to and the boundary conditions that restrain them. Therefore a considerable amount of effort is required to accurately model the structural response of these realistic structures in the loading environment for which they are expected to perform. An extraordinary amount of knowledge of the structural design details is required a priori (eg. all the local material and geometric properties of the structure, how the skins attach to the spars, what the load paths are, the nonlinearity of the joined regions, how the composite design differs from the “as built” structure, etc). In addition, the models are also only as accurate as the material properties assumed in the analysis. These material properties are usually derived from small (1 in×10 in) uniaxial coupon tests, the results of which are assumed to be appropriate for the three-dimensional structure. The development of FEM models is extremely labor intensive and requires costly experimental validation to ensure that the models accurately reflect reality.
More specifically, for real time loads associated with aircraft wings, the methodology used today relies upon conducting a fairly extensive “strain gage/loads calibration.” This method is built upon technology developed in the 1950s and, first, involves the installation of a sparsely distributed number of conventional strain gage sensors located on the inside of the wing structure. An extensive series of tests are then required to apply a matrix of independent concentrated loads to the wing surface to “calibrate’ the strain gage response to each particular load applied, called influence coefficients. Software is then used to derive loads equations that can be used in real time using the strain gage measurements as input. The drawback to this method is that it involves a considerable amount of labor and cost to perform these strain gage loads calibrations from installing strain gage instrumentation, to designing and fabricating load system hardware, to assembling the test setup, to conducting the tests, to reducing the data and deriving the loads equations. A fairly elaborate loading system is required to be designed, fabricated, and assembled in order to conduct the tests.
Due to the shortcomings of the current real time, operational loads analysis discussed above, it is desired to provide an improved, real-time, method to calculate operational load data for complex structures, and, more particularly aircraft wings, that significantly reduces time and cost.